Deletion of the 1.5 Mb tract on chromosome 17p11.2-12 that is duplicated in Charcot-Marie-Tooth disease type 1A is commonly associated with hereditary neuropathy with liability to pressure palsies. The deletion, which originates from an unequal meiotic crossover involving two homologous repeats, causes underexpression of the peripheral myelin protein gene PMP22. PMP22 frameshift and non-sense mutations can be found in the rare nondeleted cases. Targeted disruption of the PMP22 gene in mice has provided an animal model for the disease. Current studies are aimed at characterising the genetics of this chromosomal rearrangement and the pathogenic role of altered PMP22 expression.